In a switch, President Barack Obama is backing a super PAC — and directing senior government officials to appear at its fundraisers — over fears his re-election campaign could be derailed by an "avalanche" of money flowing into Republican super PACs.

Obama Campaign Manager Jim Messina announced the decision in a Monday night email titled: "We will not play by two sets of rules."

"We decided to do this because we can't afford for the work you're doing in your communities, and the grass-roots donations you give to support it, to be destroyed by hundreds of millions of dollars in negative ads. It's a real risk," Messina wrote.

The effort will include appearances at fundraisers by White House officials and members of the Cabinet, although Obama and first lady Michelle Obama will not attend them, Messina said. He also said in his email that while campaign officials will attend the fundraisers, they will not be "soliciting contributions" for Priorities USA Action, the super PAC.

He noted that Romney's super PAC raised $30 million in 2011, and has used that warchest largely for attack ads.

Obama himself has strongly criticized the Citizens United decision that created the political action committees, even upbraiding the Supreme Court during a State of the Union address as they sat before him.

Messina said Obama favors a new law — or a constitutional amendment if necessary — to place limits on spending and require full disclosure of all donations.

Messina said Republican groups are expected to spend more than $500 million, which he said is more than the Obama campaign and the Democratic National Committee are expected to raise for the president's re-election.

Just hours before the announcement late Monday night, Vice President Joseph Biden had a different message at a Florida fundraiser.

Biden said Republican super PACs would spend $200 million to $800 million to defeat the president, but the Democrats would win with volunteers.

"We can't match their multimillionaires writing $2, $5, $10, $20 million checks, but we can match every dollar they put out there with somebody on the ground," Biden said, according to a pool report.